BACKGROUND: Validation of carotid duplex ultrasound velocity criteria (CDUS VC) to grade the severity of extracranial carotid artery stenosis has traditionally been based on conventional angiography measurements. In the last decade, computed tomographic angiography (CTA) has largely replaced conventional arch and carotid arteriography (CA) for diagnostic purposes. Given the low number of CA being performed, it is impractical to expect noninvasive vascular laboratories to be validated using this modality. CDUS VC have not been developed with the use of CTA-derived measurements. The objective was to determine optimal CDUS VC from CTA-derived measurements with the North American Symptomatic Carotid Endarterectomy Trial (NASCET) method for 50% and 80% stenosis. METHODS: A retrospective review of all patients who underwent CDUS and CTA from 2000 to 2009 was performed. Vessel diameters were measured on CTA, and corresponding CDUS velocities were recorded. Percent stenosis was calculated using the NASCET method. Receiver operating characteristic (ROC) curves were generated for internal carotid artery (ICA) peak systolic velocity (PSV), ICA end diastolic velocity (EDV), and ICA PSV to common carotid artery PSV ratio (PSVR) for 50% and 80% stenosis. Velocity cut points were determined with equal weighting of sensitivity and specificity. RESULTS: A total of 575 vessels were analyzed to create the ROC curves. A 50% stenosis analysis yielded ideal cut points for PSV, EDV, and PSVR of 130 cm/sec, 42 cm/sec, and 1.75. An 80% stenosis analysis yielded ideal cut points for PSV, EDV, and PSVR of 297 cm/sec, 84 cm/sec, and 3.06. CONCLUSIONS: CTA-derived CDUS VC appeared to be reliable in defining 50% and 80% stenosis in patients with carotid artery stenosis. Although CDUS VC defined in this study were different from many of the previously published VC for the same percent stenosis, there were many similarities to those reported by the Society of Radiologists in Ultrasound consensus conference. We feel that CTA should be the gold standard imaging technique for validating CDUS VC.